Iron sulphide is heated in air to form $\mathrm{A}$, an oxide of sulphur. A is dissolved in water to give an acid. The basicity of this acid is

Given: It is given a compound Iron Sulphide which is heated in air to form oxide of sulphur and then dissolved in water to give an acid.

Concept Used: Acidity/Basicity

Detailed Solution: 

The Iron Sulphide when heated in air to form oxide can be represented by chemical reaction as:

$4\mathrm{FeS}+7{\mathrm{O}}_2\to 2{\mathrm{Fe}}_2{\mathrm{O}}_3+4{\mathrm{SO}}_2$

The Oxide A $\left({\mathrm{SO}}_2\right)$ will be  dissolved in water as:

${\mathrm{SO}}_2+{\mathrm{H}}_2\mathrm{O}\to {\mathrm{H}}_2{\mathrm{SO}}_3\rightleftharpoons 2{\mathrm{H}}^{+}+{\mathrm{SO}}_3^{2-}$

Thus it releases two $H^{+}$ and it will be dibasic.